Inhibition of BACE1 Activity by a DNA Aptamer in an Alzheimer's Disease Cell Model

RNA-Based Therapies for Neurodegenerative Diseases Targeting Pathogenic Proteins

Neurodegeneration is featured by the gradual stagnation of neuronal function and structure, leading to significant motor and cognitive impairments. The primary histopathological features underlying these conditions include the cumulation of pathological protein aggregates, chronic inflammation, and neuronal cell death. Alzheimer's disease (AD) and Parkinson's disease (PD) are prominent examples of neurodegenerative diseases (NDDs). As of 2023, over 65 million people worldwide are affected by AD and PD, with the prevalence of these conditions steadily increasing over time. Interestingly, there are no effective therapies available to halt or slow NDD progression. Most approved treatments are focused on symptom management and are often associated with substantial side effects. Given these limitations, the development of novel therapeutic approaches targeting the molecular mechanisms underlying these disorders is essential. Notably, RNA-based therapeutics have recently emerged as a potential therapeutic approach for managing various neurological diseases, offering the potential for innovative molecular interventions in NDD. In this review, we have discussed the pathogenic role of various protein aggregates in NDD and highlighted emerging RNA-based strategies aimed at targeting these pathological proteins.

Single-domain antibodies and aptamers drive new opportunities for neurodegenerative disease research

Neurodegenerative diseases (NDs) in mammals, such as Alzheimer's disease (AD), Parkinson's disease (PD), and transmissible spongiform encephalopathies (TSEs), are characterized by the accumulation of misfolded proteins in the central nervous system (CNS). Despite the presence of these pathogenic proteins, the immune response in affected individuals remains notably muted. Traditional immunological strategies, particularly those reliant on monoclonal antibodies (mAbs), face challenges related to tissue penetration, blood-brain barrier (BBB) crossing, and maintaining protein stability. This has led to a burgeoning interest in alternative immunotherapeutic avenues. Notably, single-domain antibodies (or nanobodies) and aptamers have emerged as promising candidates, as their reduced size facilitates high affinity antigen binding and they exhibit superior biophysical stability compared to mAbs. Aptamers, synthetic molecules generated from DNA or RNA ligands, present both rapid production times and cost-effective solutions. Both nanobodies and aptamers exhibit inherent qualities suitable for ND research and therapeutic development. Cross-seeding events must be considered in both traditional and small-molecule-based immunodiagnostic and therapeutic approaches, as well as subsequent neurotoxic impacts and complications beyond protein aggregates. This review delineates the challenges traditional immunological methods pose in ND research and underscores the potential of nanobodies and aptamers in advancing next-generation ND diagnostics and therapeutics.

Monoclonal antibodies and aptamers: The future therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is considered the most common and prevalent form of dementia of adult-onset with characteristic progressive impairment in cognition and memory. The cure for AD has not been found yet and the treatments available until recently were only symptomatic. Regardless of multidisciplinary approaches and efforts made by pharmaceutical companies, it was only in the past two years that new drugs were approved for the treatment of the disease. Amyloid beta (Aβ) immunotherapy is at the core of this therapy, which is one of the most innovative approaches looking to change the course of AD. This technology is based on synthetic peptides or monoclonal antibodies (mAb) to reduce Aβ levels in the brain and slow down the advance of neurodegeneration. Hence, this article reviews the state of the art about AD neuropathogenesis, the traditional pharmacologic treatment, as well as the modern active and passive immunization describing approved drugs, and drug prototypes currently under investigation in different clinical trials. In addition, future perspectives on immunotherapeutic strategies for AD and the rise of the aptamer technology as a non-immunogenic alternative to curb the disease progression are discussed.

Exploring the Potential of Aptamers in Targeting Neuroinflammation and Neurodegenerative Disorders: Opportunities and Challenges

Neuroinflammation is the precursor for several neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Targeting neuroinflammation has emerged as a promising strategy to address a wide range of CNS pathologies. These NDDs still present significant challenges in terms of limited and ineffective diagnosis and treatment options, driving the need to explore innovative and novel therapeutic alternatives. Aptamers are single-stranded nucleic acids that offer the potential for addressing these challenges through diagnostic and therapeutic applications. In this review, we summarize diagnostic and therapeutic aptamers for inflammatory biomolecules, as well as the inflammatory cells in NDDs. We also discussed the potential of short nucleotides for Aptamer-Based Targeted Brain Delivery through their unique features and modifications, as well as their ability to penetrate the blood-brain barrier. Moreover, the unprecedented opportunities and substantial challenges of using aptamers as therapeutic agents, such as drug efficacy, safety considerations, and pharmacokinetics, are also discussed. Taken together, this review assesses the potential of aptamers as a pioneering approach for target delivery to the CNS and the treatment of neuroinflammation and NDDs.

Nanomedicine based strategies for oligonucleotide traversion across the blood-brain barrier

Neurological disorders are considered the most prominent cause of disability worldwide. The major hurdle in the management of neurological disorders is the existence of the blood-brain barrier (BBB), which hinders the entry of several therapeutic moieties. In recent years, oligonucleotides have gained tremendous attention for their target specificity, diminished dose and adverse effects, thereby halting disease progression. However, enzymatic degradation, rapid clearance, limited circulation and availability at the bio-active site, etc., limit its clinical translation. Nanomedicine has opened up a breadth of opportunities in the delivery of oligonucleotides across the BBB. This review addresses the pitfalls associated with oligonucleotide delivery in traversing the BBB via nanotherapeutics for the management of brain disorders. Regulatory perspectives pertaining to hastening the clinical translation of oligonucleotide-loaded nanocarriers for brain delivery have been highlighted.

BACE1 Aptamer-Modified Tetrahedral Framework Nucleic Acid to Treat Alzheimer's Disease in an APP-PS1 Animal Model

Alzheimer's disease is a neurodegenerative disease caused by excessive amyloid β protein-induced neurotoxicity. However, drugs targeting amyloid β protein production face many problems, such as the low utilization rate of drugs by cells and the difficulty of drugs in penetrating the blood-brain barrier. A tetrahedral framework nucleic acid is a new type of nanonucleic acid structure that functions as a therapy and drug carrier. Here, we synthesized a BACE1 aptamer-modified tetrahedral framework nucleic acid and tested its therapeutic effect on Alzheimer's disease in vitro and in vivo. Our results demonstrated that the tetrahedral framework nucleic acid could be used as a carrier to deliver the BACE1 aptamer to the brain to reduce the production of amyloid β proteins. It also played an antiapoptotic role by reducing the production of reactive oxygen species. Thus, this nanomaterial is a potential drug for Alzheimer's disease.

Role of MicroRNAs, Aptamers in Neuroinflammation and Neurodegenerative Disorders

Exploring the microRNAs and aptamers for their therapeutic role as biological drugs has expanded the horizon of its applicability against various human diseases, explicitly targeting the genetic materials. RNA-based therapeutics are widely being explored for the treatment and diagnosis of multiple diseases, including neurodegenerative disorders (NDD). Latter includes microRNA, aptamers, ribozymes, and small interfering RNAs (siRNAs), which control the gene expression mainly at the transcriptional strata. One RNA transcript translates into different protein types; hence, therapies targeted at the transcriptional sphere may have prominent and more extensive effects than alternative therapeutics. Unlike conventional gene therapy, RNAs, upon delivery, can either altogether abolish or alter the synthesis of the protein of interest, therefore, regulating their activities in a controlled and diverse manner. NDDs like Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, Prion disease, and others are characterized by deposition of misfolded protein such as amyloid-ß, tau, α-synuclein, huntingtin and prion proteins. Neuroinflammation, one of the perquisites for neurodegeneration, is induced during neurodegenerative pathogenesis. In this review, we discuss microRNAs and aptamers' role as two different RNA-based approaches for their unique ability to regulate protein production at the transcription level, hence offering many advantages over other biologicals. The microRNA acts either by alleviating the malfunctioning RNA expression or by working as a replacement to lost microRNA. On the contrary, aptamer act as a chemical antibody and forms an aptamer-target complex.

Current Advances in Aptamer-based Biomolecular Recognition and Biological Process Regulation

The interaction between biomolecules with their target ligands plays a great role in regulating biological functions. Aptamers are short oligonucleotide sequences that can specifically recognize target biomolecules via structural complementarity and thus regulate related biological functions. In the past ten years, aptamers have made great progress in target biomolecule recognition, becoming a powerful tool to regulate biological functions. At present, there are many reviews on aptamers applied in biomolecular recognition, but few reviews pay attention to aptamer-based regulation of biological functions. Here, we summarize the approaches to enhancing aptamer affinity and the advancements of aptamers in regulating enzymatic activity, cellular immunity and cellular behaviors. Furthermore, this review discusses the challenges and future perspectives of aptamers in target recognition and biological functions regulation, aiming to provide some promising ideas for future regulation of biomolecular functions in a complex biological environment.

Aptamers Targeting Hallmark Proteins of Neurodegeneration

Neurodegeneration is a progressive deterioration of neural structures leading to cognitive or motor impairment of the affected patient. There is still no effective therapy for any of the most common neurodegenerative diseases (NDs) such as Alzheimer's or Parkinson's disease. Although NDs exhibit distinct clinical characteristics, many are characterized by the accumulation of misfolded proteins or peptide fragments in the brain and/or spinal cord. The presence of similar inclusion bodies in patients with diverse NDs provides a rationale for developing therapies directed at overlapping disease mechanisms. A novel targeting strategy involves the use of aptamers for therapeutic development. Aptamers are short nucleic acid ligands able to recognize molecular targets with high specificity and high affinity. Despite the fact that several academic groups have shown that aptamers have the potential to be used in therapeutic and diagnostic applications, their clinical translation is still limited. In this study, we describe aptamers that have been developed against proteins relevant to NDs, including prion protein and amyloid beta (Aβ), cell surface receptors and other cytoplasmic proteins. This review also describes advances in the application of these aptamers in imaging, protein detection, and protein quantification, and it provides insights about their accelerated clinical use for disease diagnosis and therapy.

New RNA-Based Breakthroughs in Alzheimer's Disease Diagnosis and Therapeutics

Dementia is described as the fifth leading cause of death worldwide and Alzheimer’s disease (AD) is recognized as the most common, causing a huge impact on health costs and quality of patients’ lives. The main hallmarks that are commonly associated with the pathologic process are amyloid deposition, pathologic Tau phosphorylation and neurodegeneration. It is still unclear how these events are linked to the disease progression, due to the complex pathologic mechanisms. Nevertheless, several hypotheses have been proposed for a better understanding of AD. The AD diagnosis is performed by using a combination of several tools to detect β-amyloid peptide (Aβ) deposits and modifications in cognitive performance, sometimes being expensive and invasive. In the treatment field, there is still an absence of effective treatments to delay or stop the progression of the disease, with most of the approved drugs used to relieve symptoms, and all of them with significant adverse side effects. Considering all limitations, the need to establish new and more effective diagnostic and therapeutic strategies becomes clear. This review aims not only to describe the disease and its impact but also to collect the currently available diagnostic and therapeutic strategies, highlighting new promising RNA-based strategies for AD.

Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives

Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.

Recent Advancements in Electrochemical Biosensors for Alzheimer's Disease Biomarkers Detection

Background

It is estimated that the average time between the diagnosis of Alzheimer’s disease (AD) and the patient’s death is 5-9 years. Therefore, both the initial phase of the disease and the preclinical state can be included in the critical period in disease diagnosis. Accordingly, huge progress has recently been observed in biomarker research to identify risk factors for dementia in older people with normal cognitive functions and mild cognitive impairments.

Methods

Electrochemical biosensors are excellent analytical tools that are used in the detection of AD biomarkers as they are easy to use, portable, and can do analysis in real time.

Results

This review presents the analytical techniques currently used to determine AD biomarkers in terms of their advantages and disadvantages; the most important clinical biomarkers of AD and their role in the disease. All recently used biorecognition molecules in electrochemical biosensor development, i.e., receptor protein, antibodies, aptamers and nucleic acids, are summarized for the first time. Novel electrochemical biosensors for AD biomarker detection, as ideal analytical platforms for point-of-care diagnostics, are also reviewed.

Conclusion

The article focuses on various strategies of biosensor chemical surface modifications to immobilize biorecognition molecules, enabling specific, quantitative AD biomarker detection in synthetic and clinical samples. In addition, this is the first review that presents innovative single-platform systems for simultaneous detection of multiple biomarkers and other important AD-associated biological species based on electrochemical techniques. The importance of these platforms in disease diagnosis is discussed.

Identification of a novel BACE1 inhibitor, timosaponin A-III, for treatment of Alzheimer's disease by a cell extraction and chemogenomics target knowledgebase-guided method

BACKGROUND

Rhizoma Anemarrhenae (RA) has been conventionally used for treatment of Alzheimer's disease (AD) in Traditional Chinese Medicine, and thus, the active components from RA can be screened.

PURPOSE

This research aimed to identify the active components of RA and their targets and further clarify the molecular mechanisms underlying its anti-AD activity.

METHODS

First, the potential active compounds from RA were screened by neurocyte extraction and micro-dialysis methods. Second, the potential targets were predicted by a chemogenomics target knowledgebase and further explored by surface plasmon resonance and enzyme activity assays. Third, the pharmacological effects were evaluated by employing APP/PS1 transgenic mice and SH-SY5Y-APP cells. ELISAs and Western blot analyses were used to evaluate the expression of key molecules in the amyloidogenic and NMDAR/ERK pathways.

RESULTS

Timosaponin A-III (TA-III) was screened and identified as a potential active component for the anti-AD activity, and BACE1 was proven to be a potential high-affinity target. Enzyme kinetic analysis showed that TA-III had strong noncompetitive inhibitory activity against BACE1. The in vitro and in vivo assays indicated that TA-III had pharmacological effects through improving memory impairment, reducing Aβ aggregation via the amyloidogenic pathway and preventing neuronal impairment through downregulating the NMDAR/ERK signaling pathway.

CONCLUSION

TA-III targets BACE1 to reduce Aβ aggregation through down-regulating the NMDAR/ERK pathway for treating AD.

A Systematic Review of Current Progresses in the Nucleic Acid-Based Therapies for Neurodegeneration with Implications for Alzheimer's Disease

Recently, manipulation of gene expression and switching genes on or off highlight the potential of nucleic acid-based therapies (NA-BTs). Alzheimer's Disease (AD) is a common devastating neurodegenerative disease (NDs) responsible for 60-80% of all cases of dementia and predicted as a main public health concern among aged populations. The aim of this study was to outline the current research in the field of NA-BTs for the treatment of AD disabilities, including strategies to suppress the memory and learning defects, to promote recovery processes, and to reinforce social relationships in these patients. This review was performed via evaluating PubMed reported studies from January 2010 to November 2019. Also, reference lists were checked to find additional studies. All intermediation or complementarity of animal models, case-control and cohort studies, and controlled trials (CTs) on specific NA-BTs to AD were acceptable, although in vitro studies were excluded due to the considerable diversities and heterogeneities. After removing the duplicates according to preferred reporting items for systematic reviews and meta-analyses (PRISMA) instruction, we merged remaining titles across search databases. There are 48 ongoing studies related to the application of nucleic acids in the treatment and diagnosis of AD where more consideration is given to DNA targeting strategies (18 targets for vectors and aptamers), antisense oligonucleotides (10 targets), micro-RNAs mimics (7 targets), antagomiRs (6 targets), small interferences-RNAs (5 targets), as well as mRNAs (2 targets) respectively. All of these targets are grouped into 4 categories according to their role in molecular pathways where amyloid-β (18 targets), neural survival (11 targets), memory and cognition (8 targets), and tau (3 targets) are more targeted pathways, respectively. With recent successes in the systemic delivery of nucleic acids via intravenous injection; it is worth investing in the production of new-generation medicines. There are still several challenges for NA-BTs including, their delivery to the effective modulators, mass production at low cost, sustaining efficacy and minimizing off-target effects. Regarding miRNA-based therapies, given the obvious involvement of miRNAs in numerous facets of brain disease, and the many sophisticated techniques for delivery to the brain, miRNA-based therapies will make new hope for the treatment of neurological diseases such as AD.

Aptamers: A Review of Their Chemical Properties and Modifications for Therapeutic Application

Aptamers are short, single-stranded oligonucleotides that bind to specific target molecules. The shape-forming feature of single-stranded oligonucleotides provides high affinity and excellent specificity toward targets. Hence, aptamers can be used as analogs of antibodies. In December 2004, the US Food and Drug Administration approved the first aptamer-based therapeutic, pegaptanib (Macugen), targeting vascular endothelial growth factor, for the treatment of age-related macular degeneration. Since then, however, no aptamer medication for public health has appeared. During these relatively silent years, many trials and improvements of aptamer therapeutics have been performed, opening multiple novel directions for the therapeutic application of aptamers. This review summarizes the basic characteristics of aptamers and the chemical modifications available for aptamer therapeutics.

The BACE1-Specific DNA Aptamer A1 Rescues Amyloid-β Pathology and Behavioral Deficits in a Mouse Model of Alzheimer's Disease

Amyloid-β (Aβ) plaque deposits in the brain are considered to be one of the main pathological markers of Alzheimer's disease (AD). The sequential proteolytic cleavage of amyloid precursor protein (APP) by the aspartyl proteases β-site APP-cleaving enzyme 1 (BACE1) and γ-secretase produces Aβ. Therefore, BACE1 inhibition is a very attractive target for the treatment of AD. Our previous work identified a DNA aptamer named A1 that can bind to BACE1 with high affinity and specificity and exhibits a distinct inhibitory effect on BACE1 activity in an AD cell model. The purpose of this research was to test the effect of aptamer A1 in Tg6799 mice. Four-month-old Tg6799 mice were randomly divided into two groups and treated with aptamer A1 and ineffective aptamer A1scr, respectively, by intracerebroventricular injection. Subsequent behavioral experiments showed that treatment with the aptamer A1 improved the cognitive abilities of the AD mice. Western blot indicated that BACE1 and soluble amyloid precursor protein β (sAPPβ) expression significantly decreased in the A1-treated mice. Moreover, aptamer A1 reduced the content of Aβ₄₂ and the number and density of senile plaques in AD mice. Therefore, our results indicate that aptamer A1 is a novel specific and potent BACE1 inhibitor and is a promising potential target for the treatment of AD.

DNA Aptamers Targeting BACE1 Reduce Amyloid Levels and Rescue Neuronal Deficiency in Cultured Cells

β-amyloid (Aβ) plays an essential role in the pathogenesis of Alzheimer's disease (AD). Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is indispensable for Aβ production, and knockout of BACE1 has no overt phenotypes in mouse. Thus, fine modulation of BACE1 may be a safe and effective treatment for AD patients. However, the large active site of BACE1 makes it challenging to target BACE1 with classical small-molecule inhibitors. DNA aptamer can have high affinity and specificity against diverse targets, and it provides an alternative strategy to target BACE1. In this study, we used a novel cell-systematic evolution of ligands by exponential enrichment (SELEX) strategy to select specific DNA aptamers optimized to target BACE1 under physiological status. After 17 rounds of selection, we identified two DNA aptamers against BACE1: BI1 and BI2. The identified aptamers interacted with BACE1 in pull-down assay, inhibited BACE1 activity in in vitro fluorescence resonance energy transfer (FRET) assay and HEK293-APP stable cell line, reduced Aβ in the culture medium of HEK293-amyloid protein precursor (APP) stable cell line and APP-PS1 primary cultured neurons, and rescued Aβ-induced neuronal deficiency in APP-PS1 primary cultured neurons. In contrast, the identified aptamers had no effect on α- or γ-secretase. In addition, cholesteryl tetraetylene glycol (TEG) modification further improved the potency of the identified aptamers. Our study suggests that it is feasible and effective to target BACE1 with DNA aptamers, and the therapeutic potential of the identified aptamers deserves further investigation.

Aptamers and Clinical Applications

This chapter provides a brief introduction to followed by discussion of recent preclinical studies on potential aptamer drugs grouped into two broad categories, namely, “aptamer structures” and “non-ocular diseases.” Examples of aptamer-based targeting of drugs are then described. Next is an overview of the status of nearly 30 clinical trials of aptamer drugs currently listed in ClinicalTrials.gov, which is a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world, and is a service of the US National Institutes of Health. This overview includes brief descriptions of each study sponsor, aptamer drug, disease(s), and type of study, as well as separate tables for completed studies, withdrawn or terminated studies, and active studies. The final section discusses Conclusions and Prospects.

Therapeutic aptamers in discovery, preclinical and clinical stages

The aptamer field witnessed steady growth during the past 28 years as evident from the exponentially increasing number of related publications. The field is "coming of age", but like other biomedical research areas facing a global push towards translational research to carry ideas from bench- to bedside, there is pressure to show impact for aptamers at the clinical end. Being easy-to-make, non-immunogenic, stable and high-affinity nano-ligands, aptamers are perfectly poised to move in this direction. They can specifically bind targets ranging from small molecules to complex multimeric structures, making them potentially useful in a limitless variety of therapeutic approaches. This review will summarize efforts made to accomplish the therapeutic promise of aptamers, with a focus on aptamers directly acting as therapeutic molecules, rather than those used in targeted delivery of other drugs. The review will showcase representative examples at various stages of development, covering different disease categories.

Development of DNA aptamers targeting low-molecular-weight amyloid-β peptide aggregates in vitro

We have developed a novel functional nucleic acid aptamer to amyloid-β peptide 1-40 (Aβ1-40) and investigated its potential to detect Aβ peptide fragments in neuropathologically confirmed Alzheimer brain hippocampus tissues samples. Our results demonstrate that the aptamer candidate RNV95 could detect tetrameric/pentameric low-molecular-weight Aβ aggregates in autopsy hippocampal tissue from two neuropathologically confirmed Alzheimer disease cases. Although these are preliminary observations, detailed investigations are under way. This is the first demonstration of aptamer-Aβ binding in Alzheimer brain tissues.

Novel DNA Aptamers for Parkinson's Disease Treatment Inhibit α-Synuclein Aggregation and Facilitate its Degradation

Parkinson’s disease (PD) is one of the most prevalent forms of synucleinopathies, and it is characterized neuropathologically by the presence of intracellular inclusions composed primarily of the protein α-synuclein (α-syn) in neurons. The previous immunotherapy targeting the α-syn in PD models with monoclonal antibodies has established α-syn protein as an effective target for neuronal cell death. However, due to the essential weaknesses of antibody and the unique features of aptamers, the aptamers could represent a promising alternative to the currently used antibodies in immunotherapy for PD. In this study, the purified human α-syn was used as the target for in vitro selection of aptamers using systematic evolution by exponential enrichment. This resulted in the identification of two 58-base DNA aptamers with a high binding affinity and good specificity to the α-syn, with K_D values in the nanomolar range. Both aptamers could effectively reduce α-syn aggregation in vitro and in cells and target the α-syn to intracellular degradation through the lysosomal pathway. These effects consequently rescued the mitochondrial dysfunction and cellular defects caused by α-syn overexpression. To our knowledge, this is the first study to employ aptamers to block the aberrant cellular effects of the overexpressed α-syn in cells.

Biosensors for Alzheimer's disease biomarker detection: A review

Alzheimer's disease (AD) is a chronic disease amongst people aged 65 and older. Increasing evidence has illustrated that early diagnosis holds the key to effective treatment of AD. A variety of detection techniques have been developed. Biosensors are excellent analytical tools which have applications in detecting the biomarkers of AD. This review includes appropriate bioreceptors to achieve highly sensitive and selective quantification of AD biomarkers by using transducers. AD biomarkers such as tau protein, amyloid β peptides and apolipoprotein E4, are firstly summarized. The most commonly used bioreceptors, including aptamers and antibodies, are also reviewed. We introduce aptamers specific to AD biomarkers, list the sequences of aptamers designed to capture AD biomarkers and compare the properties of aptamers with those of antibodies with regard to their efficiency as bio-recognition elements. We discuss the recent progress of aptamer systems' applications in AD biomarkers in biosensing. The review also discusses novel strategies used for signal amplification in sensing AD biomarkers.

Nucleic acid aptamers for neurodegenerative diseases

The increased incidence of neurodegenerative diseases represents a huge challenge for societies. These diseases are characterized by neuronal death and include several different pathologies, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, Huntington's disease and transmissible spongiform encephalopathies. Most of these pathologies are often associated with the aggregation of misfolded proteins, such as amyloid-ß, tau, α-synuclein, huntingtin and prion proteins. However, the precise mechanisms that lead to neuronal dysfunction and death in these diseases remain poorly understood. Nucleic acid aptamers represent a new class of ligands that could be useful to better understand these diseases and develop better diagnosis and therapy. In this review, several of these aptamers are presented as well as their applications for neurodegenerative diseases.

Nucleic Acid Aptamers: Emerging Applications in Medical Imaging, Nanotechnology, Neurosciences, and Drug Delivery

Recent progresses in organic chemistry and molecular biology have allowed the emergence of numerous new applications of nucleic acids that markedly deviate from their natural functions. Particularly, DNA and RNA molecules-coined aptamers-can be brought to bind to specific targets with high affinity and selectivity. While aptamers are mainly applied as biosensors, diagnostic agents, tools in proteomics and biotechnology, and as targeted therapeutics, these chemical antibodies slowly begin to be used in other fields. Herein, we review recent progress on the use of aptamers in the construction of smart DNA origami objects and MRI and PET imaging agents. We also describe advances in the use of aptamers in the field of neurosciences (with a particular emphasis on the treatment of neurodegenerative diseases) and as drug delivery systems. Lastly, the use of chemical modifications, modified nucleoside triphosphate particularly, to enhance the binding and stability of aptamers is highlighted.

Nucleic Acid-Based Theranostics for Tackling Alzheimer's Disease

Nucleic acid-based technologies have received significant interest in recent years as novel theranostic strategies for various diseases. The approval by the United States Food and Drug Administration (FDA) of Nusinersen, an antisense oligonucleotide drug, for the treatment of spinal muscular dystrophy highlights the potential of nucleic acids to treat neurological diseases, including Alzheimer's disease (AD). AD is a devastating neurodegenerative disease characterized by progressive impairment of cognitive function and behavior. It is the most common form of dementia; it affects more than 20% of people over 65 years of age and leads to death 7-15 years after diagnosis. Intervention with novel agents addressing the underlying molecular causes is critical. Here we provide a comprehensive review on recent developments in nucleic acid-based theranostic strategies to diagnose and treat AD.

Aptamer and its applications in neurodegenerative diseases

Aptamers are small single-stranded DNA or RNA oligonucleotide fragments or small peptides, which can bind to targets by high affinity and specificity. Because aptamers are specific, non-immunogenic and non-toxic, they are ideal materials for clinical applications. Neurodegenerative disorders are ravaging the lives of patients. Even though the mechanism of these diseases is still elusive, they are mainly characterized by the accumulation of misfolded proteins in the central nervous system. So it is essential to develop potential measures to slow down or prevent the onset of these diseases. With the advancements of the technologies, aptamers have opened up new areas in this research field. Aptamers could bind with these related target proteins to interrupt their accumulation, subsequently blocking or preventing the process of neurodegenerative diseases. This review presents recent advances in the aptamer generation and its merits and limitations, with emphasis on its applications in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, transmissible spongiform encephalopathy, Huntington's disease and multiple sclerosis.